488 EXPLANATION OF THE FIGURES. . 



FIG. 



3. Portion of the membrane of a similar embryo-sac ruptured by gradually 



increased pressure. Numerous actively-multiplying cells are forced out 

 from the fissure of the membrane; the cells also attached to the inner 

 side of the wall have been detached from it by the pressure, x 200. 



4. Longitudinal section of an embryo-sac, for the second time partly filled 



with cellular tissue ; in the middle of May of the second year. The 

 detached membrane of the embryo-sac lies iu folds near it, x 50. 



5. Young corpusculum, detached, with some of its neighbouring cells ; at the 



end of May. At this time the connection of the individual cells of the 

 endosperm is still very loose, x 300. 



6. Longitudinal section of the upper part of an endosperm; end of May. 



Two young corpuscula are visible. The cells covering the apex of the 

 latter have not yet divided by cross longitudinal septa, x 150. 



7. Transverse section through the same part of the less developed endosperm, 



on May 27th. The observer is looking from below into four corpuscula 

 opened by the section. The large nuclei attached to the inner arch of 

 the apex are visible, x 200. 



8. Longitudinal section of a corpusculum at the beginning of June, x 200. 

 8 4 . The rosette of cells covering the apex of the corpuscula, seen from above, 



x 200. 



9. Longitudinal section of a corpusculum, at the top of which the end of a 



pollen-tube has just arrived, x 200. 

 10. The lower end of a corpusculum just impregnated, with the germinal vesicle 



pressed into the arch (on the 16th June), X 300. 

 11 — 13. Stages of development of the pro-embryo (the lower ends of the 



longitudinally-divided corpuscula), from the 16th to the 18th June of 



the second year, x 300. 



PLATE LXI. 



1. Apical arch of a longitudinally- divided corpusculum of Pinus Abies, L. 



(Pirns excelsa, DC.), at which the end of a pollen-tube has lately 

 arrived, and in which several germinal vesicles adhere, of which one has 

 increased largely in size ; on the 23rd June (1858), x 500. 



2. Longitudinal section of the upper part of an endosperm of the same species 



at the same time. Two impregnated corpuscula are opened by the 

 section. In the one to the right the rudiment of a pro-embryo is 

 pressed into the lower end ; in that to the left a similar rudiment is still 

 at some distance from tbe base, x 40. 

 2*. The rudiment of the pro-embryo of this latter corpusculum, x 500. 



Pigs. 3—11. Pinus Strokes. 



3. A germinal vesicle just impregnated; on the 26th of June, X 200. 



4 — 7. A series of stages of development of the pro-embryo, arranged accord- 

 ing to their state of advancement (from 25th to 28th June). Pigs. 

 4— 6, x 300; fig. 7, x 200. 



8. The pro-embryo immediately before dividing into four longitudinal rows of 

 cells, x 100. 



